Gas-strengthened steam foam well cleaning

ABSTRACT

In cleaning a contaminant-containing conduit, steam is circulated to heat the contaminating materials and a gasstrengthened steam foam is circulated into and out of the contaminant-containing portion of the conduit to entrain and remove heated contaminants.

United States Patent Smith et al. 14 1 Dec. 26,1972

1541 GAS-STRENGTHENED STEAM FOAM 3,530,939 9 1970 Turner et al ..l66/312WELL CLEANING 3,549,420 12/1970 Cunningham. .....l34/22R 3,565,1772/1971 l'lutchison ..l66/3l2 [72] mffia' 'g' 3,637,021 1 1972 Hutchisonet a1 ..134 22 c 9 V Lawson, both of Houston, Tex.

[73] Assignee: Shell Oil Company, Huston, Tex. Primary Examiner-MarvinA. Champion [22 Filed: Oct 1 1971 I Assistant Examiner-Jack E.Attorney-Harold L. Denkler et al. 21 Appl. No.: 185,815

- [57 ABSTRACT S 4 23; In cleaning a contaminant-containing conduit,steam is [58] i R C 166/288 circulated to heat the contaminatingmaterials and a ,36 309, 312; 5 3 B, gas-strengthened steam foam iscirculated into and out 175/64 71 of the contaminant-containing portionof the conduit to entrain and remove heated contaminants.

[56] References Cited m UNITED STATES PATENTS 10 Claims, No Drawings3,410,344 11/1968 Cornelius ..166/303 l 3,412,793 11/1968 Needham..l66/270 GAS-STRENGTHENED STEAM FOAM WELL CLEANING BACKGROUND OF THEINVENTION This invention relates to cleaning conduits, such asboreholes, tubing strings, flow lines etc., in and around oil wells. Itis particularly applicable to conduit-cleaning operations in fieldlocations from which viscous oils are produced by means of asteam-heated oil recovery process.

Conduit-cleaning operations are often employed in a well to removevarious types of solid and/or liquid contaminants such as fill or debrisinvolving sand grains and/or intergrannular cementing materials or thelike solids from the reservoir formation, rust and scale or corrosionproducts from equipment within the wells, viscous and/or solidifiedorganic or inorganic materials, or the like. In such well cleaningoperations, fluids are usually circulated into and out of thecontaminant-containing portions of the wells (usually by a flow downthrough a pipe string and up through the annular space between thatstring and the next larger pipe string or the borehole wall) to entrainand remove the contaminants. US. Pat. No. 3,463,23 l describes awell-cleaning procedure in which the circulated fluid is a gas-inliquidfoam that contains specified foam stability-imparting types andproportions of aqueous liquids, surfactants and gas. Such agas-in-liquid foam is generally effective in entraining and liftingdiscrete particulate solid contaminants and displacing mobile liquidcontaminants but is relatively ineffective with respect to detachingand/or mobilizing viscous liquids or relatively low melting solids suchas viscous oils, tars, asphaltenes, waxes, etc., that stick to the wallsof the well conduits such as screens, liners, perforated casings, etc.A]- ternatively, using steam as a well-cleaning fluid is efi'ective inreleasing and/or mobilizing meltable solids or viscous liquids but isrelatively ineffective in lifting and removing solid contaminants.

The presentinvcntion is, at least in part, based on a discovery thatwhen the interior of a contaminant-containing conduit is steam heatedand a gas-strengthened steam foam is formed from amixture of steam and arelatively non-condensible gas in proportions that maintain a selectedhigh temperature while increasing the strength of the foam, thegas-strengthened steam foam can be circulated through the conduit toentrain andremove steamheated contaminants while keeping them hot andpreventing their resolidification and sticking together or sticking tothe walls of the conduits or other relatively immobile materials. Fieldtests'using a gas-strengthened steam foam to clean a well through whicha viscous oil was produced have demonstrated an efficient entrainmentand removal of contaminants in the foam of desegregated solids andthermally mobilized liquids. In those tests during a shut down of thesteam foam circulating the static, weight-supporting strength of thegas-strengthened steam foam proved to be such that the entrained solidsremained suspended in and on a column of foam and were immediatelydischarged when additional foam was pumped into the well. In cleaningsimilar wells with conventional gas-inliquid foams, the contaminantsthat were removed were removed in the form of relativelylarge aggregatesof solidified organic and inorganic materials.

2 SUMMARY OF THE'INVENTION This invention relates to cleaning conduit.The conduit and the contaminants it contains are heated by contactingthem with steam. The steam heated contaminants are entrained and removedby circulating a preformed gas-strengthened steam foam into and out ofthe contaminant-containing portion of the conduit. The gas-strengthenedsteam foam is a steam foam that contains a relatively small buteffective proportion of gas that is non-condensible at the temperatureand pressure of the conduit-cleaning operation. The proportion of gas issufficient to increase the steam foam strength (e.g., as represented bythe density, viscosity or static wei t-supporting capacity of the foam)while maintaining a selected relatively high temperature. Thegasstrengthened steam foam has a foam strength that is high relative tothat of a gas-free steam foam of otherwise similar composition,temperature and pressure.

In conducting the present invention, the steam used to heat thecontaminants within the well and/or to form a gas-strengthened steamfoam can comprise substantially any dry, wet, superheated or low-gradesteam in which the condensate and/or liquid components are compatiblewith and do not inhibit the foam producing properties of a foam-formingsurfactant. Particularly in field locations in which steam-heatedthermal oil recovery processes (such as steam drives, steam soaks,

} etc.) are conducted, the steam can advantageously be formed by therelatively high capacity steam generator utilized for the oil recoveryoperations.

In a steam generating device, the generation of steam is accompanied bya fluid volume expansion of about 1,000 times during the conversion ofaqueous liquid to vapor. At least some of the energy involved in such asteam generation fluid expansion can be used directly as the drivingforce for displacing fluid through a conduit by connecting the steamgenerating device to the conduit in a manner such that fluid displacedfrom the steam generating device is conveyed into the conduit.Alternatively the thermal energy imparted to the steam during itsgeneration can be used indirectly as the driving force for displacingfluid through a conduit by expanding the steam within pistons, turbinesor the like to drive a pumping device arranged to displace fluid intothe conduit.

In a preferred embodiment of the present invention, a steam foam isdisplaced through a hot conduit by flowing fluid from a steam generatingdevice into contact with a foam forming surfactant to form a steam foam,flowing the steam foam into the hot conduit and displacing steam foaminto the conduit in response to energy imparted to the steam during itsgeneration. And, in particular a preferred-embodiment, the steam foam isdriven into the conduit by interconnecting the steam generating deviceand the conduit so that the fluid displaced from within the steamgenerating device is displaced into the conduit. Such a direct orindirect use of the steam generation energy can also be used to displacesteam into the conduit to heat materials within a conduit. Such a use ofsteam generating energy to displace steam arfd/or steam foam into aconduit to be cleaned is particularly valuable in utilizing relativelycompact steani'generating equipment in place of relatively bulky andexpensive gas-compressing equipment in order to drive the steam foamthrough the conduit. In locations in which steam-heated thermal recoveryprocesses are operated, suitable steam generating equipment may beavailable where the cleaning is to be conducted. In such cleaningoperations the steam foam is preferably a gas-strengthened steam foam inwhich a relatively small proportion of gas is added by means of arelatively small compressor and/or tanks of pressurized gas or by meansof air and/or gas generating components mixed with the foam formingsurfactant materials.

In conducting the present process in a situation in which a relativelyhigh temperature is desired (for example, in order to melt a relativelyhigh melting solid),

' the preheating steam and gas-strengthened steam foam operation.

The gas used to form gas-strengthened steam foam can comprisesubstantially any gas which is substantially non-condensible at thetemperature and pressure of the cleaning operation and is compatiblewith the foam forming surfactant and-other components of the steam foam.Such gas can comprise air, nitrogem'carbon dioxide, methane, flue gas,ammonia, lower amines, etc. In most situations, air is preferred.

in general, in a steam foam, the temperature of the foam issubstantially equal to the boiling point of the liquid-phase componentsof the foam at the pressure of the vapor of those components. Where, forexample, the liquid-phase components of a steam foam contain a material,such as alcohol, which forms a low-boiling azeotrope with water, thefoam temperature is substantially-the boiling temperature of theazeotrope, rather than the boiling temperature of water. Similarly,where the-steam in a steam foam is mixed with noncondensible gas, theeffective pressure relative to the vaporization of the liquid componentsof the foam is the partial pressure of the steam in the mixture. In sucha situation, where the proportion of non-condensible gas is significant,the temperature of the foam is significantly lower than that of anotherwise similar gas-free steam foam. in certain situations it isdesirable to lower the temperature of a steam foam at a given pressure.For example, it may be desirable to clean a conduit at a relatively highpressure but relatively low temperature in order to melt and entrain aheat-sensitive contaminant without exceeding its decompositiontemperature. Or, as described in US. Pat. No. 3,412,793, in asteamfoam-plugging of a reservoir thief zone, it may be desirable toincrease the life span of a portion of a steam foam that remainssubstantially stationary within relatively cool surroundings in whichthe foam temperature is reduced by the heat lost to the surroundings.The life span of a so-positioned and cooled steam foam is longer if thecondensation temperature of the steam foam is lower. Such an adjustmentof the steam foam condensation temperaturecan be effected byareotropically lowering the boiling point of the liquid phase of thefoam and/or by lowering the partial pressure of the steam in the gasphase by adding a significant proportion of non-condensible gas.

In respect to conduit cleaning operations, particularly those in wellsor similar situations where a significant foam strength is needed toentrain and carry solid contaminants, applicants discovered that arelatively small proportion of non-condensible gas provides a relativelylarge increase in the foam strength without significantly lowering thecondensation temperature of ble gas per parts of steam cause asignificant im provementin the strength of a steam foam. In addition insuch proportions, the non-condensible gas causes only a relativelyinsignificant lowering in the temperature of the steam foam. In apreferred embodiment of the present process, the proportion'ofnon-condensible gas to be used can be determined by comparing thestrengths of steam foams containing various proportions of the gas andselecting a proportion which provides a foam strength exceeding that ofa gas free steam foam having substantially the same temperature at thesame pressure.

in forming a gas-strengthened steam foam in accordance with the presentprocess, the noncondensible gas can be mixed into the steam foam innumerous ways. For example, air can be compressed and pumped into asteam generator (or conduits upstream of the generator). The pressure onthe liquid in a bottled gas container of nitrogen, carbon dioxide, orthe like can be released to the extent that displaces such a gas intothe steam generator. Gas generating chemicals such as water solublebicarbonates and/or ammonium salts, or the like, can be dissolved orentrained in an aqueous liquid which contains or is mixedwith thesurfactantcontaining liquid and is flowed into the steam generatingmeans.

The liquid used to form the gas-strengthened steam foam can besubstantially any. liquid that containsa significant proportion of waterandv is miscible with water and is compatible with a foam formingsurfactant. Examples of such liquids include water, aqueous solutionscontaining water soluble salts such as alkali metal or ammonium salts,aqueous solutions containing water miscible solvents such as alcohols,glycols, ketones, alkehydes, and the like.

The surfactants used to form the gas-strengthened steam foam cancomprise substantially any foam-forming surfactant that can be dissolvedor dispersed in an aqueous liquid system. In general anionic, nonionicor cationic surfactants can be used, but the anionic surfactants, suchas sodium dodecyl benzene sulfonates, are preferred. Particularlysuitable surfactants comprise mixtures of alkali metal salts ofpetroleum sulfonates and sulfated polyoxyalkylated alcohol surfactants,such as the mixtures described in the J. Reisberg, G. Smith and J. B.Lawson U.S. Pat. No. 3,508,612. Suitable sulfonate surfactants arecommercially available as Petroleum Sulfonates from Bray ChemicalCompany, Bryton Sulfonates from Bryton Chemical Company, Petronates andPyronates from Sonneborn Division of Witco Chemical Company, PrornorSulfonates from Mobil Oil Company and the like. Surfactant sulfates ofethoxylated alcohols are available as Neodols from Shell ChemicalCompany, Tergitols from Union Carbide and the like. Suitable soap typesurfactants include sodium oleates, the soaps of tall oil heads etc.,such as those commercially available as Acintol Heads from ArizonaChemical Company, etc. Cationic surfactants such as quaternary ammoniumsalts (e.g., Redicots E- l 1 from Armour Chemical Company) and the likesurfactants can also be used.

In a preferred operating procedure, the present invention can bepracticed with equipment which is generally available in a fieldlocation, particularly in a location in which a steam heated thermal oilrecovery is in operation. A well cleaning work string, or fluid inflowpipe string, can be run in and manipulated by equipment such as agin-pole or simple production hoist. The work string can comprise aspooled continuous string of pipe which can be advanced or withdrawn bya pipe snubber. Any necessary drilling can be accomplished by means of aworkover rig. In general, a pipe string is run into the well to becleaned to a depth that is near the contaminants or fill within thewell. The steam and the gas-strengthened steam foam are circulated downthat pipe and up the annulus and the pipe is lowered as required to keepit near the top of the layer of contaminants being removed.

In a preferred operation, a steam generator that is adapted to produce awet steam such as about an 80 percent quality or low-grade steam, isconnected to flow steam into a foam generating means. The foamgenerating means can comprise a screen or porous frit or an eductorupstream of flow baffles, or the like. An air compressor or other sourceof compressed gas is connected to flow gas into the foam generatingmeans. A pumping means is arranged to flow a chemical solutioncontaining an aqueous dispersion of surfactant into the foam generatingmeans. Steam is circulated into and out of the well against a backpressure sufficient to maintain a steam pressure corresponding to thetemperature selected for the well cleaning operation within the well.When steam is returning at substantially steam temperature, the fluidbeing inflowed into the well is converted to the gas-strengthened steamfoam that is produced by the foam generator. The flow rates of thesteam, gas and chemical solution entering the foam generating means arecoordinated with respect to the temperature and pressure of the wellcleaning operation. For example, for operations at' pressures of fromabout 100 1,000 psi, suitable ranges of proportions for the componentsof the gas-strengthened steam foam comprise from about 0.2 15 standardcubic feet of gas per 100 standard cubic feet of steam and from about0.5 100 standard cubic feet of steam per gallon of liquid chemicalsolution with the chemical solution containing from about 0.5 to 5percent by weight of foam-forming surfactant.

FIELD TESTS This invention was tested by circulating a gasstrengthenedsteam foam as the drilling and cleaning fluid used in drilling out about250 feet of fill of a varied but undetermined composition in a wellapproximately 1,000 feet deep. The drilling was accomplished with aworkover rig using the steam foam as a drilling fluid, circulating downthe drill pipe and up the annulus between the drill string and an 8 inchcasing. An air compressor was set to deliver about 30 standard cubicfeet per minute of air at a pressure of about 200 pounds per square inchand was connected to a foam generating device comprising a small bafflefilled chamber. Containers and pumping means were ranged for delivery ofaqueous surfactant solution to the foam generator and a field locatedsteam generator capable of converting about 1,000 barrels per day offeed water to percent quality steam was connected so that selectedproportions of its output could be supplied to the foam generator.

In an initial test, a foot run of dirty, rusty, oily, 2- inch diameterpipe was laid on the surface and connected to the downstream end of thefoam generator. The steam generator was adjusted to apply about 25percent of its output and an aqueous solution of 30 pounds of SiponateDS-l0 and 15 poundsv of Neodol 25-38 surfactants in 200 gallons of freshwater was injected into the foam generagor at about 1 gallon per minute.No foam appeared at the outflow end of the pipe. The steam flow wasgradually decreased and the surfactant inflow rate increased until, atan air flow rate of about 30 cubic feet per minute and a steam flow ratecorresponding to about 200 barrels per day feed water conversion and asurfactant solution inflow rate of about 10 gallons per minute, a goodfoam issued from the end of the pipe. The contaminants within the pipe(viscous oil, asphaltenes, sand, etc.) were relatively quicklydischarged and the foam displaced through the pipe outflowed as a whiteapparently uncontaminated, relatively dense foamithat had the appearanceof shaving lather but which relatively quickly broke to' an aqueousliquid as it cooled to the ambient surface temperature. The foameffectively cleaned the contaminants from the pipe. Further dilutions ofthe surfactant solution were found to be possible without a significantreduction in foam strength.

In the drilling test, three 800 gallon mixing tanks were filled with a1.5 percent by weight solution of a 2 to 1 mixture of Siponate DS-lO andNeodol 25-38 surfactants. The liquid pump was set to deliver about 8gallons per minute of this solution to the foam generator. The workoverrig drill string was lowered to within about 5 feet from the top of thefill at a depth of about 860 feet. In order to heat the well, steam wasintroduced at a rate of about 150 ,barrels of water per day untilsubstantially all of the materials within the conduit to be cleaned (the8-inch well casing were heated to steam temperature as evidenced by thesteam outflow from the 4-inch blooey line connected to the wellhead.

While continuing the same rate of steam injection, the injection of thesurfactant and air were started with the air being injected at about 30standard cubic feet per minute. After about 30 minutes of substantiallyno outflow a stream of liquid appeared, became a stream of thin slurrythen a dark brown slurry which appeared to be relatively viscous and tocontain bubbles. Drilling was then initiated and the outflowing fluidduring the first feet of drilling varied from water, oil, fine sand,drilling mud and the like. During about the first 120 feet of drillingthe outflowing fluid became a viscous white foam. This foam resembledshaving grains which were to some extent coated with asphaltenes ortars. The drilling out of the 250 feet of fill required a total of abouthours and removed about 80 cubic feet of debris consisting of sand,gravel, asphaltenes, viscous oil, etc.

During the time-periods (e.g.-, 30 minutes) in which the pipeconnections were broken to add additional sections of drill pipe, it wasobserved that the foam in the hot drill pipe and annulus had a holdingcapacity and a static strength sufficient to retain the suspendedsolids. Each time steam foam circulation was resumed, entrained solidswere discharged substantially immediately indicating that they had beensupported in the column of foam standing in the annulus.

The so-cleaned well has been returned to production and is performingwell. A production increase of from about barrels per day to about 30barrels per day resulted from the cleaning operation. The materialsremoved during the steam foam cleaning were significantly morecompletely desegregated than those ordinarily removed duringconventional gas foam cleaning operations in similar wells.

What is claimed is:

l. A conduit cleaning process comprising:

flowing steam into a contaminant-containing portion of aconduit tocontact and heat the contaminants; and

circulating a preformed, gas-strengthened, steam and gas in liquid foaminto and out of the contaminant-containing portion of the conduit toentrain and remove steam-heated contaminants.

2. The process of claim 1 in which the ratio of gas to steam in thegas-strengthened steam foam is one that enhances the strength of thefoam relative to the strength of a gas-free steam foam of otherwisesimilar composition at substantially the same temperature and pressure.

3. The process of claim 2 in which said conduit is I located in a welland the steam and gas-strengthened steam foam are circulated from asurface location to the contaminant-containing portion of the conduitand back to a surface location against a back pressure corresponding tothe pressure of steam at a temperature selected for a well cleaningoperation.

4. The process of claim 3 in which a relatively noncondensible gas,steam and an aqueous liquid solution of foaming surfactant are flowedthrough a surfacelocated foam generating means to form saidgasstrengthened steam foam.

5. The process of claim 4 in which said gasstrengthened steam foamcontains from about 0.2 15 volumes of relatively non-condensible gas pervolumes of steam.

6. In a process for circulating foam through a relatively hot conduit,the improvement comprising:

flowing steam from a steam generating device into contact withfoam-forming surfactant to form a steam foam; flowing the steam foaminto the conduit; and utilizing energy imparted to the steam. during itsgeneration to drive steam foam into the conduit. 7. The process of claim6 in which noncondensible gas is mixed with said steam and surfactant toform a gas-strengthened steam foam having a strength exceeding thatof agas-free steam foam of otherwise similar composition at substantiallythe same temperature and pressure.

8. In a steam driven process for circulating hot fluid through a conduitthe improvement which comprises:

flowing steam from a steam generating device into a conduit to heat thematerial in the conduit to substantially a steam temperature;

subsequently flowing said steam into contact with foam-formingsurfactant to form a steam foam; flowing the steam foam into theconduit; and utilizing energy imparted to the steam during itsgeneration to displace steam foam into the conduit.

9. The process of claim 8 in which non-condensible gas is mixed withsaid steam and surfactant to form a gas-strengthened steam foam having astrength exceeding that of a gas-free steam foam of otherwise similarcomposition at substantially the same temperature and pressure.

10. The process of claim 9 in which the steam foam is displaced into theconduit by interconnecting the steam generating device and the conduitso that fluid displaced from within the steam generating device is dis!placed into the conduit.

2. The process of claim 1 in which the ratio of gas to steam in thegas-strengthened steam foam is one that enhances the strength of thefoam relative to the strength of a gas-free steam foam of otherwisesimilar composition at substantially the same temperature and pressure.3. The process of claim 2 in which said conduit is located in a well andthe steam and gas-strengthened steam foam are circulated from a surfacelocation to the contaminant-containing portion of the conduit and backto a surface location against a back pressure corresponding to thepressure of steam at a temperature selected for a well cleaningoperation.
 4. The process of claim 3 in which a relativelynon-condensible gas, steam and an aqueous liquid solution of foamingsurfactant are flowed through a surface-located foam generating means toform said gas-strengthened steam foam.
 5. The process of claim 4 inwhich said gas-strengthened steam foam contains from about 0.2 - 15volumes of relatively non-condensible gas per 100 volumes of steam. 6.In a process for circulating foam through a relatively hot conduit, theimprovement comprising: flowing steam from a steam generating deviceinto contact with foam-forming surfactant to form a steam foam; flowingthe steam foam into the conduit; and utilizing energy imparted to thesteam during its generation to drive steam foam into the conduit.
 7. Theprocess of claim 6 in which noncondensible gas is mixed with said steamand surfactant to form a gas-strengthened steam foam having a strengthexceeding that of a gas-free steam foam of otherwise similar compositionat substantially the same temperature and pressure.
 8. In a steam drivenprocess for circulating hot fluid through a conduit the improvementwhich comprises: flowing steam from a steam generating device into aconduit to heat the material in the conduit to substantially a steamtemperature; subsequently flowing said steam into contact withfoam-forming surfactant to form a steam foam; flowing the steam foaminto the conduit; and utilizing energy imparted to the steam during itsgeneration to displace steam foam into the conduit.
 9. The process ofclaim 8 in which non-condensible gas is mixed with said steam andsurfactant to form a gas-strengthened steam foam having a strengthexceeding that of a gas-free steam foam of otherwise similar compositionat substantially the same temperature and pressure.
 10. The process ofclaim 9 in which the steam foam is displaced into the conduit byinterconnecting the steam generating device and the conduit so thatfluid displaced from within the steam generating device is displacedinto the conduit.